Control systems for providing hydraulic control of valves from the surface are known. One example is the PES “SCRAMS” system which provides electro-hydraulic control of in-well valves from the surface. This system has solenoids which are supplied at a voltage of 120 volts for operating valves at 3,000 to 4,000 psi. Other systems are based on using electrical energy only to control valve operation and do not require hydraulic control. This means that a higher voltage, for example, 400 DC is needed to generate sufficient power to operate the valves. In practice, this is achieved by the use of a downhole power supply system incorporating high power electronic components in the downhole tool.
It is well known that downhole valves and monitoring systems have to operate at high temperatures. Electronic components operating at high temperatures are often prone to failure. This is because most normal electronic components are designed to operate at temperatures well below most oil/gas well temperatures, and the mean time below failure (MTBF) of the components falls rapidly as the environmental temperature which the components are exposed to, exceeds the design temperature. This problem is particularly acute where high voltage/currents are applied due to high electrical stresses and the operation of additional local heat by the components.
In some existing systems the size of the cable, and the conductors within the cable also limits the power which can be supplied to the cable and consequently increasing the power supply to the downhole control system has been problematic. Increasing the cross-section of the cable can result in a much more expensive cable, which is difficult to obtain and to integrate with existing systems, which require a “standard” cable size to be used.
In addition, with existing systems there is a limit to the number of devices or valves which can be driven from a single power supply. The current limit is about four to five devices and also the maximum power which can be used with the electrical only supply is about 400 volts DC. This makes it difficult to use valves above a certain size which may be required in a certain situation. Also, existing systems cannot power-up during deployment for safety reasons which means that it is not possible to monitor the downhole valves during deployment.
An object of the present invention is to provide an improved control and monitoring system for wells which obviates or mitigates at least one of the disadvantages associated with existing systems.
A further object of the present invention is to provide an improved power supply for use with an in-well flow control system which obviates or mitigates at least one disadvantage associated with existing power supplies.